Rosetta finds lost Philae weeks before mission end

By Tereza Pultarova

Published Tuesday, September 6, 2016

The Philae lander which bounced off the surface of Comet 67P/Churyumov-Gerasimenko almost two years ago to land in an unknown location has been discovered in images captured by the Rosetta spacecraft weeks before the mission’s end.

Although scientists were able to receive data from Philae, they could only identify its location indirectly and approximately from radio data. Yesterday, the European Space Agency revealed that an object, which it is certain is the lost lander, has been spotted in high-resolution images captured by Rosetta’s OSIRIS camera.

The camera captured the image of the three-legged one-metre in size Philae stuck in a crack on the comet’s surface from the distance of 2.7km.

"This wonderful news means that we now have the missing 'ground-truth' information needed to put Philae's three days of science into proper context, now that we know where that ground actually is," ESA's Rosetta project scientist, Matt Taylor, said in a statement.

Despite the less than perfect landing on 12 November 2014, Philae performed its primary scientific sequence as planned, sending data for three days while its battery lasted. However, as the probe was shaded from the Sun, its solar panels weren’t able to produce enough power and Philae switched into hibernation soon after.

As the comet moved closer to the Sun, the spacecraft woke up briefly and sent some data to the scientists in June and July 2015. It hasn’t communicated since.

“With only a month left of the Rosetta mission, we are so happy to have finally imaged Philae, and to see it in such amazing detail,” said Cecilia Tubiana of the OSIRIS camera team, the first person to have seen the images when they were downlinked from Rosetta.

It’s a symbolic end to the groundbreaking mission, which represented the first time a man-made object had been soft-landed on a surface of a comet. The research team say they are now ready to retire the orbiter without regret.

"Now that the lander search is finished we feel ready for Rosetta's landing, and look forward to capturing even closer images of Rosetta's touchdown site,” said Holger Sierks, principal investigator of the OSIRIS camera.

On 30 September, researchers will let Rosetta spiral towards the comet’s surface. They will attempt to capture some final close-up images of certain regions that could provide some more data about the comet’s geology.

Even though the 100kg Philae provided less data than the teams hoped for, the information it sent to Earth is reshaping thinking about comets.

The engineers have also learned valuable lessons for future missions. The reason why Philae bounced off during primary touchdown at a carefully selected location was the result of its three harpoon-like legs failing to attach to the comet's surface.